This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-257405, filed Sep. 10, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a multi-point distance measuring apparatus designed to selectively measure the distances to a plurality of points displayed in the finder frame for high-speed focusing and a camera mounted therewith.
Conventionally, the distance measuring apparatus to be mounted on a camera is primarily designed for spot distance measuring, that is, for measuring the distance to a single point (distance measuring point) in a small central area of the picture to be taken (finder screen). Recently, however, the multi-point distance measuring has come to be adopted, the multi-point distance measuring being designed for measuring the distances to plural points within a picture area so that the camera can be focused on a principal subject of picture to be taken regardless of the relative position of the principal subject to other subjects within the picture area.
FIG. 24A shows a case in which there are provided three distance measuring points, one at the center, the other one on left-hand side of the central point and another one on the right-hand side of thereof respectively, while FIG. 25 shows a distance measuring process according to a prior art illustrated by its routine process.
As shown in FIG. 24A, to find the distances to the three distance measuring points, C, L and R, set within the finder screen respectively, first the range to the distance measuring point L is determined out of the three distance measuring points C, L and R by means of integral control, correlation computation and interpolation computation. Similarly, distances to the point C and the point R are determined by the integral control, correlation computation and interpolation computation respectively. Then, the distance to the principal subject in the picture to be taken is selected from the results of the computations (the distances) with respect to the distance measuring points.
A multi-point distance measuring method is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 10-142490. This distance measuring method is designed for accurately determining the focal point adjusting amount and the exposure amount by specifying the principal subject of the picture to be taken by utilizing the division of the picture area based on a system wherein, with respect to a picture to be taken including plural subjects lying at equal distances in a scope of picture to be taken, the picture to be taken (the depth of field) is divided into plural sub-areas according to the distance measuring points in order to obtain the distance distribution information based on the distances determined according to the distance measuring points and the peak-value frequency distribution based on the distance distribution information.
In the case of such a passive type multi-point distance measuring apparatus, each time the distance to a distance measuring point has to be determined, complex calculation processes such as the picture element integral control, correlation computation, interpolation computation and the like are necessary.
Of these computations, the computation for integral control is a method used for limiting the voltage signal within the dynamic range of the processing circuit when storing the output current of the picture elements constituting the sensor arrays in a capacitor for conversion into electric voltage to be detected after receiving the optical image signal of the subject by two sensor arrays.
In the case of this processing method, in order for the distance to any one distance measuring point to be determined, the integral control, correlation computation and interpolation computation are necessary. Further, these computations cannot be carried out simultaneously and thus are required to be carried out sequentially. Therefore, the greater the number of distance measuring points in an area to be covered in a picture, the higher the distance measuring accuracy, but, on the other hand, it is necessary to repeat the computation for distance measuring an number of times thereby giving rise to a problem that a long time is required for distance measuring.
Further, the correlation computation is applied in determining the relative shift x between the positions images on the respective sides of the two sensor arrays, that is, the relative disagreement between the image on the side of sensor array 2a and the image position on the sensor array 2b in terms of the pitch unit of the picture element (FIG. 4) when the image signals as are shown in FIGS. 5A and 5B are received.
More particularly, the differences among the data of individual light receiving elements of the sensor arrays are measured and added; the differences among the data of individual light receiving elements b are measured and added on the same basis, provided that 1 picture element is shifted; these processes are repeated as calculations; when two image signals coincide with each other, this is considered to indicate that the correlation between these two image signals is sufficiently high to determine an approximate value of the shift x. When the shift is made for appropriate number of picture elements, both the data coincide with each other, and the sum equals to MIN value to prove a best correlation. However, when the sum is not xe2x80x9c0xe2x80x9d, it may be considered that there is a shift smaller than the pitch of the picture elements, indicating the necessity of further interpolation computation.
Repeating such complex calculations a number of times, as in the case of FIG. 24B where 30 distance measuring points are set, it takes 10 times the length of the time required in the case where 3 distance measuring points are set as in the case of FIG. 24A.
However, mere reduction of the distance measuring points can result in an adverse effect such that the principal subject is out of focus if it is located out of the distance measuring points.
Therefore, even in the case of the art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-142490, in calculating the distances to the distance measuring points on the time division basis, the calculation of the distance distribution takes a long time. Thus, when (the distance measuring system) is mounted on a camera, it takes a long time from the push at shutter to the point of exposure, causing possible miss of a good timing for clicking shutter.
An object of the present invention is to provide a camera with a multi-point distance measuring apparatus, designed for providing plural distance measuring points within a given picture area, the distance measuring apparatus comprising: a position detector for outputting the information concerning the positions of the distance measuring points-within a given picture area; a multi-point photometer for outputting the information concerning the luminance of the incident light on the distance measuring point; and a priority determiner for determining the priority of the distance measuring computation for the distance measuring points.
The camera with the multi-point distance measuring apparatus as described above is designed to selectively decide the order of distance measuring according to the relative position of the plural points and the luminance distribution of incident light within the scope of the picture in measuring the distance of the plural points within the scope of the picture to be taken. Further, the distance measuring apparatus mounted on a camera designed for sequentially measuring the distance of n number of points within a scope of the picture to be taken is provided with a priority-basis operation means designed for selecting a specific point out of plural points on the basis of the subject point and the luminance distribution within the scope of the picture to be taken, for example, in selecting the M-th point out of N number of points. Such a camera with the multi-point distance measuring apparatus is capable of effecting the integral control of the light receiving elements of all the distance measuring points, deciding the priority of the distance measuring point according to the luminance distribution within the scope of the picture to be taken, performing the correlation computation in the order of the priority of individual distances and performing an interpolation calculation as to (the points) within a predetermined range. Thus, a high-speed focusing can be realized by omitting the distance measuring operation for the points of low priority.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.